The present invention relates to a selectively soluble polymer capable of
binding to one or more constituents in a mixture containing various
biological materials and the methods of using such a polymer to purify a
biomolecule from such a mixture. The polymer is soluble in the mixture
under a certain set of process conditions such as pH or temperature and
is rendered insoluble and precipitates out of solution upon a change in
the process conditions. While in its solubilized state, the polymer is
capable of binding to a selected entity within the stream such as
impurities (DNA, RNA, host cell protein, endotoxins, etc) in a cell broth
and remains capable of binding to that entity even after the polymer is
precipitated out of solution. The precipitate can then be filtered out
from the remainder of the stream and the desired biomolecule is recovered
and further processed.